EP0575715B1 - Procedure and equipment for avoiding inrush currents - Google Patents

Abstract

A device for avoiding switching-on current surges when switching on an inductive electrical power supply apparatus (2) has an AC switch (9), which is connected in series therewith, and a phase-gating circuit (19) by means of which the connection of the electrical power supply apparatus to the mains power supply AC voltage (3, 4) can be set from the switching-on moment (7) using unipolar phase sections of equal magnitude. Furthermore, a switching means (12) is provided for driving the phase-gating circuit (19). This switching means (12) allows a predetermined number of unipolar sections of equal magnitude to be produced. The oppositely polarised half cycle which then follows immediately in time is switched with a triggering (turn-on) signal of 170 to 180 DEG . In the phase-gating circuit (19), in each case one triggering signal is produced at the predetermined phase-gating angle in each of the half cycles following this half cycle. In consequence, irrespective of the remanence (which is produced by a preceding switching off operation) of the electrical power supply apparatus, dimming, for example, of low-voltage lighting systems (illumination systems) or the connection of a welding transformer is reliably ensured in a simple manner and using few electronic modules, without any switching-on surge currents occurring. <IMAGE>

Description

The invention relates to a method for avoiding inrush current according to the preamble of claim 1 and a device for carrying out the method according to the preamble of claim 3. Such a method and such a device are known from WO-A-91/17597.

In previous switch-on methods, the circuits have stressful or even destructive switch-on peak currents that are asymmetrical in their polarity. WO-A-91/17597 (or also DE-PS 40 19 592) solves these problems by preferably switching on unipolar voltage sections with voltage sections that increase continuously. The transformer response is continuously measured by detecting the reactive current pulses. When such a small switch-on peak reactive current occurs, the transformer is switched on in full phase opposition.

This device has the disadvantage that a scanning circuit comprising many elements must be provided, which makes this device complex for large-scale applications.

Starting from this prior art, the invention is based on the object, a method and a To create device of the type mentioned. which allow an inductance-powered power supply unit to be fed with cut mains half-waves and, in a simpler and less complex manner, to ensure that a switch-on peak current which destroys a fuse and jeopardizes the circuit is reliably avoided.

According to the invention, this object is achieved by a method having the features of claim 1.

Through the use of unipolar cut half-waves in succession, the angular value of which is constant, the inductive power supply device is slowly brought into a defined position of the remanence, regardless of the original switch-on phase position and position of the remanence in the transformer. The number of gates is chosen so large that a negative remanence can be safely shifted to a positive remanence in the case of positively polarized voltage sections. Appropriate polarity reversal must be provided when selecting negative voltage sections.

Thus, after a number of cut half-waves, which depend on the type and location of the remanence of the power supply device, small and the circuit occur reactive currents that are not hazardous. If the remanence has an opposite polarity, then these reactive currents do not occur in any or only in the last section or sections, while a remanence that already has the same polarity leads to the occurrence of reactive currents over almost the entire setting time.

This avoids recording the reactive current generated during magnetization as a sign of the beginning saturation.

However, the method according to the invention makes it possible to use a circuit that is very simple and tricky in its simplicity. The above-mentioned object is namely achieved for a device for inrush current avoidance suitable for carrying out the method according to claim 3.

The number of sections and the size of the unipolar gate angle to be used depends on the inductivity-dependent power supply device. The larger the voltage section, the fewer sections are necessary to lead a transformer beginning with inverted remanence into the remanence suitable for connection. Using a larger section then leads to higher reactive currents when the remanence is reached, so that a compromise between the two sizes must be chosen.

Dispensing with a circuit for detecting an overcurrent makes it possible to use a different and very simple circuit, in particular in comparison to DE-PS 40 19 592, which leads to component and manufacturing savings, particularly in large series production. These savings are possible because the type of the power supply device to be connected, which is subject to inductance, is known in large series and therefore the sizes and angles and number of sections mentioned can be securely preset.

Further advantageous embodiments of the invention are characterized in the subclaims.

Fig. 1

ein Blockschaltbild einer Vorrichtung zur Begrenzung von Einschaltstromspitzen auf der Primärseite eines Transformators gemäß einem Ausführungsbeispiel der Erfindung, und

Fig. 2

Signalkurven der Netzspannung sowie des Netzstromes bei dem Einschalten des Transformators mit einer Vorrichtung nach Fig. 1.

An exemplary embodiment of the invention is explained in more detail below using the drawings as an example. Show it:

Fig. 1

a block diagram of a device for limiting inrush current peaks on the primary side of a transformer according to an embodiment of the invention, and

Fig. 2

Signal curves of the mains voltage and the mains current when the transformer is switched on with a device according to FIG. 1.

1 shows a block diagram of a device for limiting inrush current peaks on the primary side 1 of a transformer 2 according to an embodiment of the invention. The transformer 2 represents a possible inductance-related power supply device, which e.g. can also be formed by an inductive load.

The line voltage present at contacts 3, 4 feeds an advantageously ironless power supply unit, which provides the positive operating voltage, which is not shown in FIG. 1, for the circuit shown in FIG. 1. The plug contact 4 is connected to the circuit ground 6, while the other plug contact 3 leads to the mains voltage 5 via a mains switch 7 and to the primary winding 1 of the transformer 2, to which a load 8 can be connected on the secondary side.

The second plug connector on the primary side of the transformer 2 is connected to the circuit ground 6 via an AC switch 9 in the form of a triac, in the place of which two thyristors can also be used.

A power supply detection 10 generates a fast and dynamic power on detection signal when the power switch 7 is closed. This signal is led out via a control line 11 and, in a manner to be explained below, in particular ensures that the AC switch 9 is only switched on when all circuit components have a secure power supply.

On the one hand, this signal acts on the reset input of a timer 12, e.g. in the form of a mono flop, and resets it. Furthermore, a flip-flop 13 is reset with this signal and a possible switching operation is prevented and finally an AND gate 15 is connected via an inverter 14, so that during the first e.g. 20 milliseconds of voltage applied, the AND gate 15 as an enable and disable gate effectively prevents the AC switch 9 from being switched on.

During this start-up time of the circuit, the timer 12 switches its inverted output 16 to a level zero signal and holds it. This signal exists over a time period 30 shown in FIG. 2, which can be set with the aid of a setting potentiometer 17. In addition to the illustrated use of a mono-flop 12, any simple RC combination can also be used which has a voltage profile over time which allows a switching threshold to be exceeded or fallen short of.

The level zero signal present for the predetermined time 30 is connected in an AND gate 18 to the output signal of a gate control circuit 19. However, the switching element 13 connected to this AND gate 18 can only switch over after the above-mentioned period 30 has elapsed.

Until then, the signal generated by the gate control circuit 19 acts on an OR gate 21 connected to the output 20 of the flip-flop 13, which is then connected to the ignition input of the AC switch 9 via the switch-on protection gate 15 already mentioned.

The gate control circuit 19 can e.g. be realized by the integrated circuit TCA 785 from Siemens. The synchronization input 22 of the gate control circuit 19 is connected to the mains operating voltage 5 via a line 23.

With the gate control circuit 19, a level one signal for a constant unipolar portion 31 can be generated, as is shown in FIG. 2. The positive section 31 shown here can of course also be inverted in other embodiments of the invention, in which case the other components must be adapted accordingly. An RC circuit, not shown in the figures, is preferably provided, which is constructed in particular from a parallel connection of a resistor and a capacitor, and simulates a line voltage leading a few angular degrees at the synchronization input 22 of the gate control circuit 19, so that the thyristor release time at the end of each line half-wave is compensated and therefore the ignition signal ends somewhat before the actual network half-wave.

For example, a ramp generator is provided in the gate control circuit 19. The maximum voltage and the decay behavior of the signal ramps, for example in the form of a saw tooth, can be determined using the ramp resistance potentiometer 24 adjustable, whereby a pulse is generated each time the ramp is exceeded or undershot.

A pulse is only generated in a unipolar manner, the pulse duration being defined in such a way that the pulse length is always extended to the zero crossing of the half wave 32 just present. Since the triac 9 is ignited with the switching pulses on line 25 and must be prevented that an impulse on line 25 which is still in the zero crossing of the AC line voltage 33 can ignite the triac 9, the RC circuit simulating a leading mains voltage 33 is in front of the Synchronization input 22 of the gate control circuit 19 has been arranged. Thus, the pulse present on line 25 surely ends a few degrees before each zero crossing 34 of the AC mains voltage 33.

Thus, after the start time specified by the voltage supply detection 10 has expired, unipolar ignition signals at a specific angle 35 generated by the gate control circuit 19 are applied to the AC switch 9 for the duration of the time specified by the timing element 12, which means in for the time specified by the angle 35 Every second half-wave the transformer 2 is connected to the network.

The mode of operation of this connection is easier to explain in connection with FIG. 2.

2 shows profiles of the mains voltage 33 and of the primary-side current 36 when the transformer 2 is switched on.

The sinusoidal curve 33 shows the AC mains voltage, which is switched off at any time, which in particular does not have to coincide with the end of a half-wave. In FIG. 2, the hatching between the abscissa and the curve 33 means that the mains voltage is detected by the voltage power supply and is therefore applied to the primary winding of the transformer 2.

After the random switch-off of the mains voltage 33, the transformer 2 is switched on before the end of the positive half-wave 32 of the mains voltage 33, which begins at a point in time 37.

The hysteresis curve 50 of the transformer 2, ie the induction field strength diagram, has a point 51 when switched on, which indicates the remanence resulting from the switching off. In the case shown in FIG. 2, the transformer 2 has a negative remanence 51. The gate control circuit 19 switches through the voltage section 35 to the transformer 2 in the positive half-wave 32. The voltage section 35 is arranged before the transition from the positive half-wave 32 to the negative half-wave 38. This increases the field strength 52 in the positive range, the induction 53 simultaneously changing in the direction of more positive values. After the end of the half-wave 32 and thus the end of the connection of the voltage section 35, the magnetization state in the iron of the transformer returns to a remanence 61 which has a somewhat higher induction 53 which is shifted in the positive direction.

This process is not associated with the occurrence of a reactive current 36.

In the subsequent positive half-waves 32, the described process is repeated, so that after passing through the described curve, in which the field strength 52 increases together with the induction density 53, the remanence 71, 81 and 91 is somewhat more positive than before. After here e.g. five full waves, the remanence 91 has almost reached the operating magnetization curve 50. In each subsequent section 35, it then runs on the hysteresis curve 50, starting from the remanence 101 then at the end of section 35, i.e. the zero crossing 39, in the maximum operating induction 102, i.e. a saturation field strength 104, which corresponds to the maximum operating current induction, is reached. A reactive current 40 then occurs each time, which does not endanger the circuit and the consumer because it corresponds to the no-load current of an inductive load.

After the time period 30 has elapsed, the timer 12 switches back during the occurrence of a section 35 and the flip-flop 13 switches on, so that an ignition signal is present at the zero crossing 39 and all subsequent zero crossings, so that the consumer in With respect to the last positive half-wave 32 in the following opposite phase 41 is fully switched on. The magnetization state of the iron in the transformer 2 then runs through the hysteresis curve up to the negative operating induction 103 and back.

After each application of the voltage time area to the transformer 2, the remanence 51 increases somewhat to more positive values until it runs into the positive maximum operating induction 102 via the intermediate points 61, 71, 81, 91 and 101. The remanence 51 etc. increases as a result of an increase in the field strength, which decreases in the manner of a magnetic spring during the rest period to the next section 35, and because a higher induction 53 also leads to a higher remanence 61 etc. . The rest time remaining at an AC voltage of 50 Hertz, e.g. 15 milliseconds is more than sufficient for the magnetization to migrate back to the remanence point on axis 52. The specified turn-on time of 5 milliseconds corresponds to a gate angle of 90 degrees.

The respective section 35 has a predetermined size, with which a field strength 52 which is less than or at most equal to the saturation field strength 104 is generated in each case in the case of the predefined inductivity power supply device 2. This limits the reactive currents to size 40, which occur when saturation is reached. The section 35 is advantageously between 10 and 90 degrees. With this choice, with a rest period in between, the magnetization can spring back like a spring and there is no integration of the unipolar voltage sections and therefore no magnetizing field strength.

The number of half-waves 32, ie the number of connections, is chosen to be so large that, in the case of the section 35 of predetermined size, one of the polarities of the Section 35 inverted remanence 51 of the inductivity power supply device 2, ie the worst case and shown in FIG. 2, can be safely converted into the magnetization of the same polarity. This means that for the specified section 35, which specifies the maximum reactive current 40, the number of sections 35 is preset until 30 reactive currents 40 occur in one or more half-waves 32 at the end of the period. This must be determined for a transformer 2 in series production and can then be preset for the entire series.

By specifying a larger section 35, a higher reactive current 40 is accepted, whereby section 35 should not increase field strength 52 above saturation field strength 104. At the same time, the time until the device is switched on in the opposite phase 41, i.e. the number of sections 31 is reduced. On the other hand, a smaller section 35 leads to smaller reactive currents 40 as soon as the transformer 2 goes into saturation, but the time which is necessary to set the positive remanence 101 reliably at an unfavorable starting point as in FIG. 1 is extended. A possible time for the period 30 is e.g. 0.5 seconds. This would result in an order of magnitude of 25 sections 35.

After the time 30 specified by the switching means 12 has elapsed, the turn-on circuit 19 can also generate a turn-on angle of less than 180 degrees, for example in the range from 150 to 180 degrees for turning on in the opposite phase and for further operation. A complete connection of the opposite phase is not Necessary if the other half-waves are also less than 180 degrees and their angular value is in particular smaller than the phase connection.

If a larger switch-on angle for switching on in the opposite phase 41 can be generated with the phase gating circuit 19 and an ignition signal can be generated in the phase gating circuit 19 for the half-waves following the phase-opposite half-wave 41, then such a device can e.g. can be used for dimming.

In other embodiments, it can be provided that in the phase control circuit 19 an ignition signal can be generated with the actuator 29 at a predetermined phase control angle which does not correspond to 180 degrees, i.e. it is also possible to supply a consumer 8 with cut half-waves. In particular, the first phase-opposite section must be larger than the following operating sections in order to symmetrize the hysteresis around the zero point.

It is also possible to bypass the thyristor circuit 9 in accordance with a device in DE 41 32 208 of the applicant, in which, after fully switching on, the thyristor circuit is bridged by a relay in the time segment 35, in which case the thyristor 9 is saved for the half-phase connection in phase opposition.

The operation detection circuit 10 can have a voltage comparison device with which a reduced faulty value can be compared by a voltage comparison Mains voltage is detectable. If such a faulty and smaller line voltage 5 is detected, the switching means 12 is then switched on with a new delay to restart the connection. The restart reliably prevents the two successive half-waves, which are polarized opposite to the faulty mains voltage half-wave, drive the transformer 2 into saturation.

Of course, the principles of the invention can also be applied to three-phase devices. If the power supply device is a three-phase power supply device, an alternating current switch 9 is interposed between the mains and the three-phase power supply device for each or at least two branches of the three-phase power supply device, with which the gate control circuit 19 supplies the one alternating current switch 9 with the corresponding switching signals in parallel, and the other alternating current switch 9 after one e.g. is activated in the applicant's WO91 / 17597 delay time.

Claims (8)

1. Method of avoiding a current inrush when an inductance-loaded power supply unit (2) is switched on, which is connected in series with an a.c. switch (9), wherein unipolar voltage sections (31) are generated by means of a phase sectioning circuit (19) for connecting said inductance-loaded power supply unit (2) to the alternating mains voltage from the switch-on moment onwards, with said inductance-loaded power supply unit (2) being switched on with a succession of unipolar voltage sections (31) of substantially equal widths,
   characterised in
   that the width of said voltage section (31) is so selected that the magnetic field strength, which is generated by said unipolar voltage sections (31) will not be increased above the field strength (52) which corresponds to the maximum operating inductance (102) of said inductance-loaded power supply unit (2), and that after a predetermined settable number of switch-on operations with said unipolar sections of equal width, which number depends on said inductance-loaded power supply unit (2), the circuit is switched on with a sectioned half-wave, e.g. for dimming, or with a complete half-wave (41) during the phase opposition then following, without measuring the reactive current.
2. Method of according to Claim 1, characterised in that the number of switch-on operations is selected to be so great that at the section of predetermined size a remanence which is inverted relative to the polarity of the sections of said inductance-loaded power supply unit may be reliably passed over into the homopolar magnetisation when the system is switched on.
3. Device for avoiding a current inrush when an inductance-loaded power supply unit (2) is switched on, which is connected in series with an a.c. switch (9), including a phase sectioning circuit (19) for setting the connection of said inductance-loaded power supply unit (2) with the alternating mains voltage (3, 4) via the a.c. switch (9) from the switch-on moment (7) onwards only with firing signals for unipolar voltage sections (31) of substantially equal widths, for carrying through the method according to any of Claims 1 and 2,
   characterised in
   that switching means (12) are provided which may be used to switch on said inductance-loaded power supply unit (2) after a Seattle number (30) of switch-on operations (31), which is determined by said inductance-loaded power supply unit (2), with said unipolar sections (35) of equal widths, without measuring the reactive current in phase opposition (41), wherein the width of said voltage sections (31) is selected by means of a potentiometer (24) in a way that the magnetic field strength created by said unipolar voltage sections (31) will not be increased above the field strength (52) corresponding to the maximum operating inductance (102) of said inductance-loaded power supply unit (2).
4. Device according to Claim 3, characterised in that upon expiration of the period (30) predetermined by said switching means (12) a wider sectioning angle may be generated by means of said phase sectioning circuit (19) for switch-on in phase opposition (41), and that a firing signal may be generated at a predetermined smaller phase sectioning angle in said phase sectioning circuit (19) at each of the half-waves following the antiphase half-wave (41).
5. Device according to Claim 3 or Claim 4, characterised in that said switching means (12) is a timer element suitable to set a leading interval (30) during which the desired number of the succession of substantially equal unipolar switch-on sections (35) may be generated.
6. Device according to any of Claims 3 to 5, characterised in that an operation detector circuit (10) is provided which may be used to switch on said switching means (12) with a delay for generating said equal unipolar switching sections (35) by means of said phase sectioning circuit (19).
7. Device according to Claim 6, characterised in that a reduced faulty mains voltage may be detected by voltage comparison by means of said operation detector circuit (10), with said switching means (12) being adapted for switch-on with a delay for restart of the switch-on operation.
8. Device according to any of Claims 3 to 7, characterised in that said power supply unit is a three-phase power supply, and that for each branch or at least two branches of said three-phase power supply a respective a.c. switch (9) is interposed between the mains and said three-phase power supply.

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